Boundary Layer Measurements on the BOLT II Geometry Using Pressure and Temperature Sensitive Paints

Hypersonic vehicles are subjected to an extreme aerothermodynamic environment dominated by intense thermal loading which is amplified further when the local boundary layer state transitions from a laminar to a turbulent state. Due to weight and complexity considerations, it is not feasible to incorporate thermal protection systems (TPS) over an entire hypersonic body. Therefore, it is critically important to identify and predict where the boundary layer will undergo transition such that the thermal protection system can be focused on the most at-risk areas. This work attempts to observe boundary layer transition on the Boundary Layer Transition (BOLT) II flight test model, which is a canonical geometry developed by the Air Force Office of Scientific Research in conjunction with Johns Hopkins Applied Physics Laboratory. Multiple non-intrusive optical diagnostics are utilized in a Mach 4 and Mach 7 Ludwieg tubes at the University of Tennessee Space Institute including pressure and temperature sensitive paint as well as molecular tagging velocimetry. Previous work on the BOLT II geometry is discussed and the results of this work are compared to relevant similar experiments. This work found that temperature sensitive paint was most successful in observing the complex flow structures that lead to the break down to transition. The diagnostic paint results presented here compare favorably to previous work, especially computational efforts from the University of Minnesota.